ADC0809 VHDL控制程序
--文件名：ADC0809.vhd
--功能：基于VHDL语言，实现对ADC0809简单控制
--说明：ADC0809没有内部时钟，需外接10KHz~1290Hz的时钟信号，这里由FPGA的系
--统时钟（50MHz）经256分频得到clk1（195KHz）作为ADC0809转换工作时钟。
--最后修改日期：2004.3.20
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
use ieee.std_logic_arith.all;
entity ADC0809 is
  port (   d       : in std_logic_vector(7 downto 0);          --ADC0809输出的采样数据
         clk,eoc   : in std_logic;        --clk为系统时钟，eoc为ADC0809转换结束信号
clk1,start, ale,en: out std_logic;                                --ADC0809控制信号
        abc_in    :in std_logic_vector(2 downto 0);                     --模拟选通信号
abc_out     :out std_logic_vector(2 downto 0);        --ADC0809模拟信号选通信号
        q        : out std_logic_vector(7 downto 0));          --送至8个并排数码管信号
 end ADC0809;
architecture behav of ADC0809 is
type states is ( st0,st1, st2, st3, st4,st5,st6);                         --定义各状态的子类型
signal current_state, next_state:states:=st0;
signal regl :std_logic_vector(7 downto 0);                            --中间数据寄存信号
signal qq:std_logic_vector(7 downto 0);
begin
com:process(current_state,eoc)                             --规定各种状态的转换方式
begin
  case current_state is
  when st0=>next_state<=st1;ale<='0';start<='0';en<='0';
  when st1=>next_state<=st2;ale<='1';start<='0';en<='0';
  when st2=>next_state<=st3;ale<='0';start<='1';en<='0';
  when st3=>             ale<='0';start<='0';en<='0';
        if eoc='1' then next_state<=st3;                            --检测EOC的下降沿
        else next_state<=st4;
        end if;   
  when st4=>              ale<='0';start<='0';en<='0';
        if eoc='0' then next_state<=st4;                            --检测EOC的上升沿
else next_state<=st5;
end if;
  when st5=>next_state<=st6;ale<='0';start<='0';en<='1';
  when st6=>next_state<=st0;ale<='0';start<='0';en<='1';regl<=d;
  when others=> next_state<=st0;ale<='0';start<='0';en<='0';
  end case;
end process;
clock:process(clk)                 --对系统时钟进行分频，得到ADC0809转换工作时钟
begin
 if clk'event and clk='1' then qq<=qq+1;              --在clk1的上升沿，转换至下一状态
if QQ="01111111" THEN clk1<='1'; current_state <=next_state;   
  elsif qq<="01111111" then clk1<='0'; 
    end if; 
end if;
end process;
q<=regl;  abc_out<=abc_in; 
end behav;